1. Field of the Invention
The present invention relates to an optical characteristic measuring apparatus for measuring an optical characteristic of a special effect coating such as a metallic coating or a pearlescent coating having different hues depending on an illuminating direction or an observing direction.
2. Description of the Related Art
Conventionally, a metallic coating or a pearlescent coating to be used as e.g. a coating of an automobile body contains a luster material composed of aluminum flakes, mica flakes, or a like substance. An intensity of reflection light from the luster material is different depending on an observing direction because of a variation in reflection light resulting from a variation in orientations of the luster material. This enables to obtain a metallic effect or a pearlescent effect. In the case where an optical characteristic of a material such as a metallic coating or a pearlescent coating having the above property is measured, it is impossible to evaluate a difference in optical characteristic resulting from a variation in orientations of the luster material merely by measuring reflection light in one angular direction. Accordingly, normally, the difference in optical characteristic is evaluated by measuring reflection light in multiple angular directions. Heretofore, there has been used a multi-angle colorimeter provided with a multi-angle geometry of illuminating in multiple directions and receiving in a single direction, or illuminating in a single direction and receiving in multiple directions, as an optical characteristic measuring apparatus capable of measuring reflection light in different angular directions (see e.g. Japanese Unexamined Patent Publication No. 2006-10508). Generally, a portable or handy multi-angle calorimeter is desirable to allow an operator to perform measurement at various different measurement positions e.g. in performing measurement with respect to a surface of an automobile body, as described above.
In the case where measurement is performed by the multi-angle calorimeter, illumination in multiple directions or receiving in multiple directions is carried out during a measuring operation. This may require a relatively long measurement time. If the multi-angle colorimeter is a handy type apparatus, it is highly likely that shake or a like movement of the apparatus may occur during the measuring operation. The shake during the measuring operation is a primary cause of degrading measurement reproducibility by the multi-angle colorimeter.
In order to solve the above drawback, the following approach has been proposed. Specifically, a mechanical switch operable to be turned on and off depending on the distance between a sample and the measuring apparatus is provided near a measurement aperture portion. The operator is allowed to detect whether the measuring apparatus is tilted relative to the sample, or displaced from an intended position by monitoring a change of the mechanical switch between on and off states during a measuring operation.
In the above approach, judgment is made based on binary data by turning on and off the mechanical switch. This may require the switch to be operated for threshold value adjustment or sensitivity adjustment at the time of producing the measuring apparatus or in use of the measuring apparatus. Also, the entire part of the mechanical switch is required to be firmly contacted with a sample surface, in view of a point that the switch has a mechanical structure. Accordingly, the mechanical switch is not suitable in measuring an object to be measured having many curved portions such as a surface of an automobile body. Specifically, in the conventional measuring apparatus, positions to be measured are limited to flat plane portions. In the above arrangement, it is often the case that the operator is forced to perform measurement at a position other than a position where the operator intends to perform measurement, e.g. a position where the mechanical switch is firmly contacted with the sample surface, and the mechanical switch is allowed to be depressed.